This invention relates generally to the separation of solid particles entrained in a gas stream and, more particularly, relates to the separation of wood fibers entrained in steam so as to separate at least a portion of the steam from the remaining stream of fibers and steam.
In the manufacture of paper, wood chips are subjected to a chemical action or to a combination of mechanical and chemical action and reduced to fine fibers. Conventionally, these fibers are conveyed to a further processing station through a pipe at a velocity of between 5,000 and 30,000 feet per minute by means of steam.
When the fibers entrained in the steam flow arrive at the process station, it has been conventional to pass the entrainment of steam and fibers through a cyclone separator to separate the fiber from the steam. Alternatively, a fiber-steam separation centrifuge is described in U.S. Pat. No. 4,253,857, ('857 Patent) to separate wood fibers from steam. As described in the '857 Patent, fibers enter a housing of the centrifuge which includes a rotor in the housing. The rotor has blade tips that directly engage the fiber and steam flowing through the housing. Centrifugal forces applied by the rotor to the fibers tend to move the fibers to the outer perimeter of the housing and into a fiber discharge port of the housing. In contrast to the path of the fibers through the housing, the steam flowing through the housing is drawn towards the center of the rotor by suction created by a fan rotating in a separation chamber adjacent to the housing.
The fiber-steam separator of the type disclosed in the '857 Patent experienced difficulties due to the rubbing of the rotor blade tips against the housing and the accumulation of fibers in small voids between the edges of the rotor and the housing. Accordingly, there remains a long-felt need for an improved method and apparatus for separating fibers from steam in a stream of fibers and steam.